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Boring bar issues

I do a fair amount of boring on my 11 inch Logan. Job I in it now is 4 inch diameter 3 inch disk. Need 1 1/2 inch one end 2 1/8 other. Started with a small # 2 M/T drill worked up to 3/4 inch then Silver and Demings to 1 1/4. Then go at it with the boring bar to size.

Bar I am using is a 1 inch, 90 degree one end 45 the other. Run in a QR AXA tool post. 1/4 inch HSS bit, well ground and sharp. Itís solid no chatter.

Problem is the bits fixing screws. Two Allenís holding the bit. Very small. 2 MM Allen wrench fits it. You canít put much torque on the screws or the head strips. Correct Allen wrench clean with air hose setting up nothing keeping the screw from holding except itís so small. Working out to size the bit will slip unexpectedly, have to shut down and reset. Yesterday gave it up and used carbide tip boring bars instead.

I see two options, use the bar for light use only, but even light internal threading bit slips itís a problem. Or drill the holes out tap for a larger screw .

It just sounds like a poorly designed tool. If you could modify the bar, ..... like larger set screws or some type of clamp it may be salvageable and less aggravating to use.

I have a set of 3/8" tool holders that take a 1/4" IC insert. They came with a really small Torx type hold down screw. Couldn't really tighten it down with out stripping the head and removing it was the same problem.
Finally I found some stainless slotted flat head screws that fit and I replaced all the Torx screws. Haven't had an issue since. Perhaps you could find some replacement screws.

Using TWO setscrews to me suggests that the cutting tip is a piece of HSS rather than a carbide insert. If so I don't see any reason not to drill out and thread for bigger screws to allow using a bigger hex wrench.

I have never understood the desire to use some teeny-weeny setscrews in boring bars to hold the tool bit. I have built my own diy boring bars so that I have used M4 socket head at minimum. Might need splitted bar or some sort of wedge but 1” bar leaves plenty of room for design.

Two things:
I think your problem may be the quality of the screws.
USA made HSSS (Hex Socket Set Screws) can only be made to US Standards (ASA 1962 ie) , while foreign screws (You said metric!) "CAN" have
lower standards. There is a huge difference in strength. If you use foreign made screws, only get DIN 12.9 which is comparable to ASA 1962
. Obviously American made or DIN 12.9 are more expensive. Look for Unbrako,CamCarr,Allen or HK (HoloKrome)
Second thing
Trying to tighten a screw against a highly polished surface (HSS Toolbit) can be like slipping on ice, so you need a rougher surface.
Take the top or surface of the toolbit (where ever the screw impinges) and touch it lightly on a FINE grinding wheel to get a satin type finish to allow the screw a grip on the toolbit.
Rich

I'd make it into a split clamp and use the biggest screw I could find - that's if the hole branched for the bit is a close fit. Another option might be to put another set screw in 90deg around the bit from the others. If the two are coming in from the top, put the third in from the front of the bar. Or make an insert to go at the back end of the bit with another set screw as a backstop/ pusher. Plus make the other screws bigger

Some good tips. No doubt the small screws are Chinese Junk, for sure I am going to drill out and tap for at least 1/8 inch quality American made Allen’s, roughen up flats on the 1/4=inch HSS Bit good idea too. The pocket is tight no issue there.

Have to go any further to made it work will send it to the scrap box & start from scratch. I really prefer boring with a bit I have ground from HSS. The Chinese carbide tipped bars work but don’t leave the finish I want most times & grinding myself can use the same bar for threading